Semiconductor manufacturers are continually working to reduce time-to-market in an effort to improve serviceability while decreasing operating costs. This is particularly true for fabrication facilities that produce high volumes (on the order of 1,000 wafer starts per day) of complex products. As such, efforts have been made to develop and implement systems and methods such as continuous flow manufacturing, including operations management, which is also known as range management.
In range management systems, wafer processing is partitioned into a series of flows, where the products in each flow follow similar routes through the fabrication facility. These flows are divided into ranges, and each range may include one or more operations. An operation is where the units (e.g., wafers) of a production lot are actually worked on, and may include, for example: lithography, metrology, overlay, metrology CD, etc. Normally, a particular lot spends twenty-four hours in a range, and then is moved to the next range. Of the twenty-four hours, the lot may, for example, undergo six hours of processing time in the operations of the range, sixteen hours of non-processing time waiting in a queue, and two hours of transit time being moved between operations and/or other ranges. Thus, it is possible for numerous lots to be processed through a single range a twenty-four hour period.
Typically, new production lots are started every day, and a particular lot may undergo processing in seventy or more ranges before it is complete. Also, different lots may result in different end products, thereby requiring different operations during their manufacture. As such, there may be thousands of active lots in the fabrication facility at any one time, with those lots being dispersed amongst the numerous operations of the fabrication facility.
Range management systems are used to manage the flow of the production lots through the fabrication facility. Range management systems focus on delivering work in progress (WIP) (e.g., lots or units in a lot) on a known route at a known speed to meet committed customer deliveries on schedule. In conventional range management implementations, operators that run the various operations are given target volumes for the day and are expected to dispatch lots, as they are available, to achieve the target. There are two drawbacks associated with such implementations of range management. The first is one of control, because it is difficult to ensure that individual operators are attempting to meet the range targets. The second concerns visibility. Even if individual operators are attempting to meet the range targets, it is difficult for them to decide which lots to run to most efficiently achieve the target.
Problems with conventional range management systems also arise when a fabrication facility has alternate priority schemes that compete with range targets. In such cases, operators are forced to decide whether it is more important to run lots to achieve the range target or run a lot given a high priority for another reason (e.g., a late lot, hot lot, etc.). Further problems arise when WIP travels along non-standard (e.g., branch) routes, because existing range management systems cannot control WIP flow accurately unless the route is known.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.